| 1. |
- Aryal, Pradip, et al.
(författare)
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Comparative study of the main electromagnetic models applied to melt pool prediction with gas metal arc : Effect on flow, ripples from drop impact, and geometry
- 2022
-
Ingår i: International Journal of Heat and Mass Transfer. - : Elsevier. - 0017-9310 .- 1879-2189. ; 194
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Tidskriftsartikel (refereegranskat)abstract
- The present work concerns the electromagnetic force models in computational fluid dynamics simulations of melt pools produced with electric arcs. These are commonly applied to gas metal arcs with metal transfer, in welding and additive manufacturing. Metal drop impact on the melt pool is thus included in this study. The electromagnetic force models applied in literature use either numerical solutions of Poisson equations or one of the two analytical models developed by Kou and Sun, or Tsao and Wu. These models rely on assumptions for which the effect on the melt pool predictions remains to be understood. The present work thoroughly investigates those assumptions and their effects. It has been supported by dedicated experimental tests that did provide estimates of unknown model parameters and validation data. The obtained results show that the assumptions that fundamentally distinguish these three models change the electromagnetic force, including the relation between its components. These changes, which can also be spatially non-uniform, are large. As a result, these models lead to significantly different recirculation flow pattern, thermal convection, melt pool morphology, bead dimensions, and free surface response to the metal transfer. We conclude by proposing conditions in which each of these models is suited or questionable.
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| 2. |
- Aryal, Pradip, et al.
(författare)
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Effect of Substrate Orientation on Melt Pool during Multi-Layer Deposition in V-Groove with Gas Metal Arc
- 2021
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Ingår i: Proceedings of the World Congress on Mechanical, Chemical, and Material Engineering. - : Avestia Publishing. - 2369-8136. - 9781927877616
-
Konferensbidrag (refereegranskat)abstract
- Thermo-fluid dynamic and experimental approaches are used to investigate the influence of 20° uphill, downhill and sideway substrate orientation during metal deposition over a previously deposited bead in a V-groove. The computational fluid dynamic model with free surface deformation and metal transfer gives insight into the melt pool flow and causes of defect formation observed on the solidified beads. The experimental metallographs, high-speed images and computational results show good agreement. It is found that the deposition of a second layer on a smooth first layer cooled down to room temperature leads to large changes in melt pool flow pattern at 20° substrate inclination compared to flat condition. It results in undercut and humps with the uphill orientation and undercut with the side inclination. Therefore, lower angle range is necessary for multilayer gas metal arc deposition for these two last configurations.
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| 3. |
- Choquet, Isabelle, et al.
(författare)
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A physically based model for thermal plasma arc attachment on a W-ThO2 cathode
- 2016
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Ingår i: 2016 IEEE International Conference on Plasma Science (ICOPS).
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Konferensbidrag (refereegranskat)abstract
- Summary form only given. Arc attachment radius imposed a priori when modelling the coupling between cathode, cathode layer and thermal plasma still hinders models from being predictive, as underlined in a recent review1. The aim of this work was to find a physical element, still lacking in the models, which could contribute in governing the arc attachment. In this study the cathode layer is modeled within the frame of the partial local thermal equilibrium approach1 including the space charge layer, the Knudsen layer and the ionization layer, while the plasma column is assumed to be in local thermal equilibrium. Several modeling assumptions were questioned based on e.g. contradictory assumptions in the literature, or oversimplified physics compared to experimental observations. For testing model and assumptions, 5 mm argon arc test cases with a sharp cathode geometry that have been investigated experimentally in the literature were calculated. Within this framework, the following conclusions were drawn. The space charge emitted electrons is negligible. The Richardson-Dushman emission law supplemented with Schottky correction is used within its domain of validity when applied to thorium doped tungsten cathodes, which are mainly characterized by a field enhanced thermionic emission regime. The radiative heat absorption from the plasma at the cathode surface is not negligible compared to the radiative emission. Ignoring the non-homogeneous structure and composition of a doped tungsten cathode operated in these conditions leads to a large over-estimation of the extent of the arc attachment, and results in an under-estimation of the arc temperature. A cathode model based on physical criteria for taking into account a first level of the cathode inhomogeneity has a significant effect on the arc attachment and on arc properties such as temperature and pressure. The cathode physics is thus an important element to include for obtaining a comprehensive and predictive arc model.
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| 4. |
- Choquet, Isabelle, et al.
(författare)
-
A predictive model for gas tungsten arc heat source
- 2016
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Ingår i: The 7th International Swedish Production Symposium, SPS16, Conference Proceedings. - Lund : Swedish Production Academy. ; , s. 1-10
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Konferensbidrag (refereegranskat)abstract
- Gas tungsten arcs are used as heat sources in production processes such as welding and metal deposition.However, the most advanced of the existing gas tungsten arc models still lack predicting the arc temperature observed experimentally, unless imposing a priori the extent of the cathode arc attachment.Possible causes of this problem were investigated. It was concluded that the physical state of the arcing gas tungsten cathode was too simplified by the existing models. This oversimplification results in an overestimation of the cathode arc attachment area and an underestimation of the arc temperature field.An improved model was developed based only on physical criteria. It was tested by comparison with experimental measurements available in the literature. Good agreement with the temperature measured on the cathode surface and within the arc were obtained.
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| 5. |
- Choquet, Isabelle, et al.
(författare)
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Analysis of the Influence of the Composition of the Shielding Gas on Pressure Force and Heat Fluxes in Arc Welding
- 2014
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Ingår i: Proceedings of The 6<sup>th</sup> International Swedish Production Symposium 2014. - 9789198097412 ; , s. 1-8
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Konferensbidrag (refereegranskat)abstract
- A main problem raised by arc welding manufacturing is the determination ofthe optimal process parameters to ensure weld quality as well as resource efficient andsustainable production. To address this problem a better process understanding is required.In this study thermal magneto hydrodynamic modeling of a welding arc is used to reacha deeper insight into the influence of the composition of the shielding gas on the pressureforce and the heat fluxes to a workpiece. The model was implemented in the open sourcesimulation software OpenFOAM. Four different shielding gas mixtures combining argonand carbon dioxide were studied. When increasing the fraction of carbon dioxide the resultsshow a significant increase of the arc velocity and temperature with constriction of thetemperature field, a decrease of the pressure force and a significant increase of the heatfluxes on the base metal.
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| 6. |
- Choquet, Isabelle, et al.
(författare)
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Electric welding arc modeling with the solver OpenFOAM - A comparison of different electromagnetic models
- 2011
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Ingår i: International Institute of Welding Document No 212-1189-11, July 2011..
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Konferensbidrag (refereegranskat)abstract
- This study focuses on the modeling of a plasma arc heat source in the context of electric arc welding. The model was implemented in the open source CFD software OpenFOAM-1.6.x, coupling thermal fluid mechanics in three dimensions with electro magnetics. Four different approaches were considered for modeling the electromagnetic fields: i) the three-dimensional approach, ii) the two-dimensional axi-symmetric approach, iii) the electric potential formulation, and iv) the magnetic field formulation as described by Ramírez et al. [1]. The underlying assumptions and the differences between these models are described in detail. Models i) to iii) reduce to the same quasi one-dimensional limit for an axi-symmetric configuration with negligible radial current density, contrary to model iv). Models ii) to iv) do not represent the same physics when the radial current density is significant, such as or an electrode with a conical tip. Models i) to iii) were retained for the numerical simulations. The corresponding results were validated against the analytic solution of an infinite electric rod. Perfect agreement was obtained for all the models tested. The results from the coupled solver (thermal fluid mechanics coupled with electromagnetics) were compared with experimental measurements for Gas Tungsten Arc Welding (GTAW). The shielding gas was argon, the arc was short (2mm), the electrode tip was conical, and the configuration was axi-symmetric. The boundary conditions were specified at the anode and cathode surfaces. Models i) and ii) lead to the same results, but not the model iii). Model iii) neglects the radial current density component, resulting in a poor estimation of the magnetic field, and in turn of the arc fluid velocity. The limitations of the coupled solver were investigated changing the gas composition, and using different boundary conditions. The boundary conditions, difficult to measure and to estimate a priori, significantly affect the simulation results.
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| 7. |
- Choquet, Isabelle, et al.
(författare)
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Magnetic field models for high intensity arcs, applied to welding - A comparison between three different formulations
- 2013
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Ingår i: 9th International Conference on Trends in Welding Research; Chicago, IL; United States; 4 June 2012 through 8 June 2012. - 9781627089982 ; , s. 876-885
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Konferensbidrag (refereegranskat)abstract
- Most simulation studies done to deeper understand high-intensity welding arcs address axi-symmetric configurations and use the electric potential formulation. This formulation involves the assumption of a one-dimensional magnetic field. The assumption is justified in its original frame: rather long arcs (about 10 mm), and when the electrode tip is excluded from the computational domain. However, arcs applied to welding are shorter, and the electrode geometry is important to take into account. The present work questions the assumption of a one-dimensional magnetic field for simulating short welding arcs. We have compared three different approaches for modeling the magnetic field: three-dimensional, two-dimensional axi-symmetric, and the electric potential formulation. These models have been applied to water cooled anode Gas Tungsten Arc Welding (GTAW) test cases with truncated conical electrode tip (tip radius of 0.5 and 0.2 mm) and various arc lengths (2, 3 and 5 mm). For the axi-symmetric cases studied in the present work, the three- and two-dimensional models give exactly the same results. The one-dimensional simplification of the magnetic field turns out to have a significant unfavorable effect on the simulation results. For axi-symmetric welding applications, it is argued that the two-dimensional axi-symmetric formulation should be used.
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| 8. |
- Choquet, Isabelle, 1965-, et al.
(författare)
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Modeling and simulation of a heat source in electric arc welding
- 2011
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Ingår i: Proceedings from the 4th Swedish Production Symposium, Lund, Sweden. ; , s. 202-211, s. 201-211
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Konferensbidrag (refereegranskat)abstract
- This study focused on the modeling and simulation of a plasma heat source applied toelectric arc welding. The heat source was modeled in three space dimensions couplingthermal fluid mechanics with electromagnetism. Two approaches were considered forcalculating the magnetic field: i) three-dimensional, and ii) axi-symmetric. The anodeand cathode were treated as boundary conditions. The model was implemented in theopen source CFD software OpenFOAM-1.6.x. The electromagnetic part of the solverwas tested against analytic solution for an infinite electric rod. Perfect agreement wasobtained. The complete solver was tested against experimental measurements for GasTungsten Arc Welding (GTAW) with an axi-symmetric configuration. The shielding gaswas argon with thermodynamic and transport properties covering a temperature rangefrom 200 to 30 000 K. The numerical solutions then depend greatly on the approachused for calculating the magnetic field. The axi-symmetric approach indeed neglectsthe radial current density component, mainly resulting in a poor estimation of the arcvelocity. Various boundary conditions were set on the anode and cathode. Theseconditions, difficult to measure and to estimate a priori, significantly affect the plasmaheat source simulation results. Solution of the temperature and electromagnetic fieldsin the electrodes will thus be included in the forthcoming developments.
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| 9. |
- Choquet, Isabelle, 1965-, et al.
(författare)
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Numerical simulation of Ar-x%CO2 shielding gas and its effect on an electric welding arc
- 2011
-
Ingår i: IIW Commission XII / SG 212 Intermediate meeting, University West, Trollhättan, Sweden, 21 - 23 March 2011, IIW Doc. XII-2017-11. ; , s. 1-12
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This study focuses on the simulation of a plasma arc heat source in the context of electric arc welding. The simulation model was implemented in the open source CFD software OpenFOAM-1.6.x, in three space dimensions, coupling thermal fluid mechanics with electromagnetism. Two approaches were considered for calculating the magnetic field: i) the three-dimensional approach, and ii) the so-called axisymmetric approach. The electromagnetic part of the solver was tested against analytic solution for an infinite electric rod. Perfect agreement was obtained. The complete solver was tested against experimental measurements for Gas Tungsten Arc Welding (GTAW) with an axisymmetric configuration. The shielding gas was argon, and the anode and cathode were treated as boundary conditions. The numerical solutions then depend significantly on the approach used for calculating the magnetic field. The so-called axisymmetric approach indeed neglects the radial current density component, mainly resulting in a poor estimation of the arc velocity. Plasma arc simulations were done for various Ar-x%CO2 shielding gas compositions: pure argon ( x =0), pure carbon dioxide ( x =100), and mixtures of these two gases with x =1 and 10% in mole. The simulation results clearly show that the presence of carbon dioxide results in thermal arc constriction, and increased maximum arc temperature and velocity. Various boundary conditions were set on the anode and cathode (using argon as shielding gas) to evaluate their influence on the plasma arc. These conditions, difficult to measure and to estimate a priori, significantly affect the heat source simulation results. Solution of the temperature and electromagnetic fields in the anode and cathode will thus be included in the forthcoming developments.
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| 10. |
- Choquet, Isabelle, 1965-, et al.
(författare)
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On the choice of electromagnetic model for shorthigh-intensity arcs, applied to welding
- 2012
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Ingår i: Journal of Physics D. - : IOP Publishing. - 0022-3727 .- 1361-6463. ; 45:20, s. 205203-
-
Tidskriftsartikel (refereegranskat)abstract
- Four different approaches were considered for modelling the electromagneticfields of high-intensity electric arcs: i) the three-dimensional model, ii) the twodimensionalaxi-symmetric model, iii) the electric potential formulation, and iv) themagnetic field formulation. The underlying assumptions and the differences betweenthese models are described in detail. Models i) to iii) reduce to the same limit for anaxi-symmetric configuration with negligible radial current density, contrary to modeliv). Models i) to iii) were retained and implemented in the open source CFD softwareOpenFOAM. The simulation results were first validated against the analytic solutionof an infinite electric rod. Perfect agreement was obtained for all the models tested.The electromagnetic models i) to iii) were then coupled with thermal fluid mechanicsin OpenFOAM, and applied to the calculation of an axi-symmetric Gas Tungsten ArcWelding (GTAW) test case with short arc (2mm) and truncated conical electrode tip.Models i) and ii) lead to the same simulation results, but not model iii). Model iii)is suited in the specific limit of long axi-symmetric arc, with negligible electrode tipeffect. For short axi-symmetric arc, the more general axi-symmetric formulation ofmodel ii) should instead be used.
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| 11. |
- Dogan, Emanuel M., 1984-, et al.
(författare)
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Resuscitative endovascular balloon occlusion of the aorta in zone I versus zone III in a porcine model of non-traumatic cardiac arrest and cardiopulmonary resuscitation : A randomized study
- 2020
-
Ingår i: Resuscitation. - : Elsevier. - 0300-9572 .- 1873-1570. ; 151, s. 150-156
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Tidskriftsartikel (refereegranskat)abstract
- INTRODUCTION: Resuscitative endovascular balloon occlusion of the aorta (REBOA) in zone I increases systemic blood pressure during cardiopulmonary resuscitation (CPR), while also obstructing the blood flow to distal organs. The aim of the study was to compare the effects on systemic blood pressure and visceral blood flow of REBOA-III (zone III, infrarenal) and REBOA-I (zone I, supraceliac) during non-traumatic cardiac arrest and CPR.METHODS: Cardiac arrest was induced in 61 anesthetized pigs. Thirty-two pigs were allocated to a hemodynamic study group where the primary outcomes were systemic arterial pressures and 29 pigs were allocated to a blood flow study group where the primary outcomes were superior mesenteric arterial (SMA) and internal carotid arterial (ICA) blood flow. After 7-8minutes of CPR with a mechanical compression device, REBOA-I, REBOA-III or no aortic occlusion (control group) were initiated after randomization.RESULTS: Systemic mean and diastolic arterial pressures were statistically higher during CPR with REBOA-I compared to REBOA-III (50mmHg and 16mmHg in REBOA-I vs 38mmHg and 1mmHg in REBOA-III). Systemic systolic, mean and diastolic arterial pressures were statistically elevated during CPR in the REBOA-I group compared to the controls. The SMA blood flow increased by 49% in REBOA-III but dropped to the levels of the controls within minutes. The ICA blood flow increased the most in REBOA-I compared to REBOA-III and the control group (54%, 19% and 0%, respectively).CONCLUSION: In experimental non-traumatic cardiac arrest and CPR, REBOA-I increased systemic blood pressures more than REBOA-III, and the potential enhancement of visceral organ blood flow by REBOA-III was short-lived.
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| 12. |
- Grafver, Isabelle, 1991-, et al.
(författare)
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Intestinal fatty acid-binding protein as a potential biomarker for gastrointestinal complications after complex endovascular aortic surgery
- 2024
-
Ingår i: Annals of Vascular Surgery. - : Springer. - 0890-5096 .- 1615-5947. ; 106, s. 176-183
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVE: This study aimed to investigate the association between intestinal fatty acid-binding protein, acute gastrointestinal injury grade, and gastrointestinal complications after fenestrated or branched endovascular aortic aneurysm repair.METHODS: A total of 17 patients undergoing endovascular aortic repair for thoracoabdominal, juxtarenal, suprarenal or pararenal aneurysm between May 2017 and September 2018 were enrolled. Blood samples were collected preoperatively and during postoperative intensive care. The blood samples were analyzed for intestinal fatty acid-binding protein with enzyme-linked immunosorbent assay. Gastrointestinal function was assessed according to the acute gastrointestinal injury grade every day during postoperative intensive care.RESULTS: Higher concentrations of intestinal fatty acid-binding protein at 24 h and 48 h correlated to higher acute gastrointestinal injury grade on postoperative days 1, 2 and 3 (p=0.032 and p=0.048, p=0.040 and p=0.018, and p=0.012 and p=0.016, respectively). Patients who developed a gastrointestinal complication within 90 days postoperatively had a higher overall acute gastrointestinal injury grade than those who did not develop a gastrointestinal complication (p<0.001), as well as higher concentrations of intestinal fatty acid-binding protein at 48 h (p=0.019). Patients developing gastrointestinal dysfunction (acute gastrointestinal injury grade ≥2) had a higher frequency of complications (p=0.009) and longer length of stay in the intensive care unit (p=0.008).CONCLUSIONS: In patients undergoing endovascular aortic repair for complex aneurysm increased postoperative plasma intestinal fatty acid-binding protein concentrations and postoperative gastrointestinal dysfunction, evaluated using the acute gastrointestinal injury grade, were associated with gastrointestinal complications, indicating that these measures may be useful in the postoperative management of these patients.
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| 13. |
- Javidi-Shirvan, Alireza, 1978, et al.
(författare)
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Coupling boundary condition for high-intensity electric arc attached on a non-homogeneous refractory cathode
- 2018
-
Ingår i: Computer Physics Communications. - : Elsevier BV. - 0010-4655 .- 1879-2944. ; 222, s. 31-45
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Tidskriftsartikel (refereegranskat)abstract
- The boundary coupling high-intensity electric arc and refractory cathode is characterized by three sub-layers: the cathode sheath, the Knudsen layer and the pre-sheath. A self-consistent coupling boundary condition accounting for these three sub-layers is presented; its novel property is to take into account a non-uniform distribution of electron emitters on the surface of the refractory cathode. This non-uniformity is due to cathode non-homogeneity induced by arcing. The computational model is applied to a one-dimensional test case to evaluate the validity of different modeling assumptions. It is also applied coupling a thoriated tungsten cathode with an argon plasma (assumed to be in local thermal equilibrium) to compare the calculation results with uniform and non-uniform distribution of the electron emitters to experimental measurements. The results show that the non-uniformity of the electron emitters’ distribution has a significant effect on the calculated properties. It leads to good agreement with the cathode surface temperature, and with the plasma temperature in the hottest region. Some differences are observed in colder plasma regions, where deviation from local thermal equilibrium is known to occur.
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| 14. |
- Javidi Shirvan, Alireza, et al.
(författare)
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Effect of cathode model on arc attachment for short high-intensity arc on a refractory cathode
- 2016
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Ingår i: Journal of Physics D. - : IOP Publishing. - 0022-3727 .- 1361-6463. ; 49:3 November 2016, s. 1-17
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Various models coupling the refractory cathode, the cathode sheath and the arc at atmospheric pressure exist. They assume a homogeneous cathode with a uniform physical state, and differ by the cathode layer and the plasma arc model. However even the most advanced of these models still fail in predicting the extent of the arc attachment when applied to short high-intensity arcs such as gas tungsten arcs. Cathodes operating in these conditions present a non-uniform physical state. A model taking into account the first level of this non-homogeneity is proposed based on physical criteria. Calculations are done for 5 mm argon arcs with a thoriated tungsten cathode. The results obtained show that radiative heating and cooling of the cathode surface are of the same order. They also show that cathode inhomogeneity has a significant effect on the arc attachment, the arc temperature and pressure. When changing the arc current (100 A, 200 A) the proposed model allows predicting trends observed experimentally that cannot be captured by the homogeneous cathode model unless restricting a priori the size of the arc attachment. The cathode physics is thus an important element to include to obtain a comprehensive and predictive arc model
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| 15. |
- Javidi Shirvan, Alireza, et al.
(författare)
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Modelling of electrode-arc coupling in electric arc welding
- 2014
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Ingår i: Proceedings of The 6<sup>th</sup> International Swedish Production Symposium 2014 16-18 September 2014. - 9789198097412 ; , s. 1-8
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Konferensbidrag (refereegranskat)abstract
- Modelling of the arc in electric arc welding is significant to achieve a better pro-cess understanding, thus gain better weld quality and a more efficient production process.It requires knowing the conditions at the surfaces of the anode and cathode. These condi-tions are very difficult to set from measurements and should be calculated. This requiresmodelling the complex physics of the electrode layer coupling electrode and arc. Thispaper presents a self-consistent electrode layer model that 1) is suited to welding applica-tions, 2) accounts for the known physics taking place, and 3) satisfies the basic conservationrequirements. The model is tested for different conditions. Its potentiality for welding ap-plications is shown through calculations coupling plasma arc, electrode and cathode layermodels. The calculations are done for both tungsten and thoriated tungsten electrode.
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| 16. |
- Javidi-Shirvan, Alireza, 1978, et al.
(författare)
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Numerical modelling of shielding gas flow and heat transfer in laser welding process
- 2012
-
Ingår i: Proceedings of The 5th International Swedish Production Symposium, Linköping, Sweden. - 9789175197524 ; , s. 269-276
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Konferensbidrag (refereegranskat)abstract
- In the present study a three-dimensional model has been developed to study shieldinggas in a laser welding process using computational fluid dynamics. Laser heatingof titanium alloy Ti6Al4V was done by imposing a volumetric laser heat source. Themodel was implemented in the open source software OpenFOAM and applied to theinvestigation of the shielding gas behaviour over the base metal.Three different cases regarding the outlet shape of the shielding pipe were studied. Insome laser welding processes a shielding plate is used to help protecting the weldedarea. The plate injects the additional shielding gas screen during the welding process.This plate is also considered in the modelling as the fourth case.The influence of the shape of the pipe outlet is discussed.The simulation results confirmedthat the shielding plate can protect the welded area by covering the welding pathwith shielding gas. However, the simulation showed that the shielding gas leaving theplate flows towards the keyhole. It can thus bring some fumes over the keyhole whichis not desired since it can make it difficult to track the welding with optical method.
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| 17. |
- Katsarelias, Dimitrios, et al.
(författare)
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The Effect of Beta-Adrenergic Blocking Agents in Cutaneous Melanoma-A Nation-Wide Swedish Population-Based Retrospective Register Study.
- 2020
-
Ingår i: Cancers. - : MDPI AG. - 2072-6694. ; 12:11
-
Tidskriftsartikel (refereegranskat)abstract
- Previous studies have demonstrated an anti-tumoral effect of beta-adrenergic blocking agents on cutaneous melanoma (CM). The aim of this study was to investigate if beta-adrenergic blocking agents have an impact on survival in Swedish patients with melanoma. A population-based retrospective registry study including all patients diagnosed with a primary invasive melanoma between 2009 and 2013 was performed. Data from the Swedish Melanoma Register were linked to the Swedish Prescribed Drug Registry and the Swedish Cause of Death Register. Cox regression analyses including competing risk assessments were performed. There were 12,738 patients included, out of which 3702 were exposed to beta-blockers vs. 9036 non-exposed patients. Age, male sex, Breslow thickness, ulceration, and nodal status were independent negative prognostic factors for melanoma-specific survival (MSS). Adding beta-blockers to the analysis did not add any prognostic value to the model (HR 1.00, p = 0.98), neither when adjusting for competing risks (HR 0.97, p = 0.61). When specifically analyzing the use of non-selective beta-blockers, the results were still without statistical significance (HR 0.76, p = 0.21). In conclusion, this population-based registry study could not verify that the use of beta-adrenergic blocking agents improve survival in patients with melanoma.
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| 18. |
- Monstein, Hans-Jurg, 1946-, et al.
(författare)
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Multiple displacement amplification of DNA from human colon and rectum biopsies: Bacterial profiling and identification of Helicobacter pylori-DNA by means of 16S rDNA-based TTGE and pyrosequencing analysis
- 2005
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Ingår i: Journal of Microbiological Methods. - : Elsevier BV. - 1872-8359 .- 0167-7012. ; 63:3, s. 239-247
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Tidskriftsartikel (refereegranskat)abstract
- Amplifying bacterial DNA by PCR from human biopsy specimens has sometimes proved to be difficult, mainly due to the low amount of bacterial DNA present. Therefore, nested or semi-nested 16S rDNA PCR amplification has been the method of choice. In this study, we evaluate the potential use of whole genome amplification of total DNA isolated from human colon and rectum biopsy specimens, followed by 16S rDNA PCR amplification of multiple displacement amplified (MDA)-DNA. Subsequently, a H. pylori-specific 16S rDNA variable V3 region PCR assay was applied directly on MDA-DNA and, combined with pyrosequencing analysis; the presence of H. pylori in some biopsies from colon in patients with microscopic colitis was confirmed. Furthermore, temporal temperature gradient gel electrophoresis (TTGE) of 16S rDNA amplicons using primers flanking variable regions V3, V4, and V9, was used to establish bacterial profiles from individual biopsies. A variation of the bacterial profiles in the colonic mucosa in microscopic colitis and in normal rectal mucosa was observed. In conclusion we find the MDA technique to be a useful method to overcome the problem of insufficient bacterial DNA in human biopsy specimens. (c) 2005 Elsevier B.V. All rights reserved.
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| 19. |
- Nilsson, Håkan, 1971, et al.
(författare)
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Implementation of a 3D solver for electric arc welding, coupling fluid mechanics with electromagentics
- 2011
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Ingår i: 8th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics. HEFAT2011. ; , s. 614-620
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Konferensbidrag (refereegranskat)abstract
- This paper describes the implementation of a 3D numerical solver for electric arc welding, where the fluid mechanics of the shielding gas is strongly influenced by the electromagnetic fields. The implementation is done in the OpenFOAM-1.6.x OpenSource Computational Fluid Dynamics (CFD) tool (www.openfoam.com). OpenFOAM is basically a general library of C++ classes for numerical simulation of continuum mechanic problems, but it is mainly used in CFD. The basics of high-level programming in OpenFOAM is described briefly, while the main components of the implementation done in the present work are described in high detail. The implementation is validated against an analytical solution of the electromagnetic field of an infinite electrically conducting rod, and against an experimental study of GTAW (Gas Tungsten Arc Welding). The numerical results agree very well with both the analytical and experimental results. A grid-dependency study has been made for the GTAW case, showing that the main features of the presented solutions are independent of the mesh size.
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| 20. |
- Nilsson, Isabelle, 1971-, et al.
(författare)
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Molecular cloning of a putative Ciona intestinalis cionin receptor, a new member of the CCK/gastrin receptor family
- 2003
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Ingår i: Gene. - : Elsevier BV. - 0378-1119 .- 1879-0038. ; 323:1-2, s. 79-88
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Tidskriftsartikel (refereegranskat)abstract
- Cionin, a peptide showing similarities with cholecystokinin and gastrin has been shown to be expressed in the gut and neural ganglion of the protochordate Ciona intestinalis. The present report describes the cloning of a putative cionin receptor (CioR), a new member of the CCK/gastrin family from the gastrointestinal tract of C. intestinalis. mRNA from the stomach of C. intestinalis was isolated using a modified RNA extraction procedure and, subsequently, reverse-transcribed into single-stranded cDNA by means of rapid amplification of 5′- and 3′-cDNA ends (RACE-PCR), followed by full-length PCR amplification. The cloned full-length PCR amplicons contained a short upstream open-reading frame (uORF) coding for a putative 16 amino acid long peptide, followed by a long open reading frame encoding a 526 amino acid putative CioR protein. At the amino acid level, the putative CioR protein shared 35–40% homology with cloned mammalian, chicken, and Xenopus laevis CCK receptors. Phylogenetic analysis revealed that the chicken and X. laevis CCK receptors are orthologues of the mammalian CCK2 receptors whereas CioR protein forms a clade with vertebrate cholecystokinin receptors. Moreover, we found that the CioR cDNA and deduced amino acid sequences were found to correspond to the annotated CCK/gastrin-like receptor gene on Scaffold 117 (C. intestinalis draft genome project, Joint Genome Institute database; http://www.jgi.doe.gov).
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| 21. |
- Nilsson, Isabelle, 1971-, et al.
(författare)
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Molecular cloning of an unusual bicistronic cholecystokinin receptor mRNA expressed in chicken brain : a structural and functional expression study
- 2003
-
Ingår i: Regulatory Peptides. - 0167-0115 .- 1873-1686. ; 114:1, s. 37-43
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Tidskriftsartikel (refereegranskat)abstract
- This report describes the molecular cloning and pharmacological characterization of a transiently expressed chicken brain cholecystokinin receptor (CCK-CHR) in COS-7 cells. A polymerase chain reaction (PCR)-based cloning strategy was applied using: (1) an initial PCR with deoxyinosine-containing primers designed to target conserved regions in CCK receptors, followed by (2) rapid amplification of cDNA ends (RACE), and (3) full-length PCR of the CCK-CHR cDNA. The full-length cloned bicistronic CCK-CHR cDNA contained a short upstream open reading frame (uORF) coding for a putative six-amino-acid-long peptide of unknown function, followed by a long open reading frame (lORF) encoding the 436-amino-acid-long CCK-CHR receptor protein. At the amino acid level, the CCK-CHR shared ∼50% homology with mammalian and Xenopus laevis CCK receptors. The pharmacological profile of CCK-CHR resembled that of CCK-B receptors using agonists (CCK-8, CCK-4, gastrin-17), whereas CCK-CHR showed higher affinity for the CCK-A receptor antagonist, devazepide, than for the CCK-B receptor antagonist, l-365,260. To the best of our knowledge, this is the first description and functional expression study of a cloned chicken CCK receptor cDNA.
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| 22. |
- Nilsson, Isabelle, 1971-, et al.
(författare)
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Multiple displacement amplification of isolated DNA from human gallstones : Molecular identification of Helicobacter DNA by means of 16S rDNA-based pyrosequencing analysis
- 2005
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Ingår i: Helicobacter. - : Wiley. - 1083-4389 .- 1523-5378. ; 10:6, s. 592-600
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Tidskriftsartikel (refereegranskat)abstract
- Background. Molecular typing of Helicobacter spp. in clinical biopsy specimens has become increasingly important. By means of nested polymerase chain reaction (PCR) amplification and Southern blot analysis of the PCR amplicons, we have shown that Helicobacter spp. DNA is present in human gallstones. In this study we have investigated the possibility of using multiple displacement amplification (MDA) of isolated gallstone DNA and pyrosequencing analysis for the molecular identification of Helicobacter spp. Materials and Methods. DNA isolated from the nucleus of 33 human gallstones and one control strain were used in a MDA assay. Subsequently, pyrosequencing analysis was performed either directly on MDA-DNA using primers flanking the Helicobacter spp. 16S rDNA variable V3 region or on PCR amplicons derived from broad-range primers flanking the 16S rDNA variable V3, V4, and V9 regions. Results. Pyrosequencing analysis of 16S rDNA derived from MDA-DNA revealed that Helicobacter spp.-like DNA was present in 25 of 33 (approximately 76%) gallstones. Using an H. pylori-specific Southern blot analysis, Helicobacter spp.-like DNA was present in 20 of 33 [approximately 61%] of the gallstones. Using MDA-DNA directly in pyrosequencing analysis, Helicobacter spp.-like DNA was present in 13 of 33 [approximately 39%] gallstones. Conclusions. We conclude that multiple displacement amplification combined with pyrosequencing enables a rapid and accurate molecular typing of Helicobacter spp. from small and precious biopsy specimens. © 2005 The Authors Journal compilation © 2005 Blackwell Publishing Ltd.
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| 23. |
- Nilsson, Isabelle, 1971-, et al.
(författare)
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Pharmacological analysis of CCK2 receptor ligands using COS-7 and SK-N-MC cells, expressing the human CCK2 receptor
- 2002
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Ingår i: Regulatory Peptides. - 1873-1686 .- 0167-0115. ; 103:1, s. 29-37
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Tidskriftsartikel (refereegranskat)abstract
- A series of CCK2 receptor ligands were analysed with respect to their interaction with binding sites in the membranes of COS-7 cells and SK-N-MC cells transiently expressing the human CCK2 receptor (short isoform). The ligands were YF476, YM022, AG041R, L-740,093, JB93182, PD134308, and PD136450. Their binding was analysed by radioligand competition using [H-3]L-365,260 as the labelled ligand. Saturation binding analysis indicated that [H-3]L-365,260 interacted with a single class of binding sites. In competition binding experiments using COS-7-cell membranes, all seven ligands were incubated together with 2 nM [H-3]L-365,260. The data for four of the compounds fitted a one-site model (pK(i) values: YM022: 9.2 +/- 0.02, YF476: 9.6 +/- 0.04; L-740,093: 9.2 +/- 0.01, and AG041R: 8.3 +/- 0.06), while the data for the three others fitted a two-site model (pK(i) values: JB93182: 8.8 +/- 0.04 and 6.0 +/- 0.15; PD 134308: 9.0 +/- 0.04 and 6.1 +/- 0.15; and PD 136450: 9.0 +/- 0.02 and 5.4 +/- 0.41). SK-N-MC cell membranes and 2 nM [H-3]L-365,260 were incubated together with YM022, YF476, JB93182, and PD134308. The data for YM022 and YF476 fitted a one-site model (pKi values: YM022: 9.3 +/- 0.06, YF476: 9.4 +/- 0.02), while the data for JB93182 and PD134308 fitted a two-site model (pK(i) values: JB93182: 8.7 +/- 0.06 and 6.2 +/- 0.06; PD134308: 9.1 +/- 0.06 and 7.0 +/- 0.17). Competition binding experiments in the presence of the GTP-analogue guanylylimidodiphosphate, using either of the two cell types, produced similar binding data for PD 134308 and JB93182 as in the absence of GTP-analogue. The human receptor seems to exist in a low and/or high affinity state. The shift from low to high affinity does not seem to reflect the degree of G protein coupling.
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| 24. |
- Nilsson, Isabelle, 1971-
(författare)
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The cholecystokinin receptor family : molecular cloning and pharmacological characterization
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Cholecystokinin (CCK) and gastrin are hormones/neurotransmittors of the gastrointestinal tract and central nervous system. The receptors for gastrin and CCK are members of the G protein-coupled receptor family. The aim of this study was to clone and pharmacologically characterize vertebrate and invertebrate CCK receptors and splice variants. Three 5'-end alternatively spliced human CCK2 receptor mRNAs were cloned: the CCK-BRwt mRNA, that encodes the ordinary full-length CCK2 receptor, CCK-BRt mRNA that contains exon 1b and that encodes a N-terminally truncated receptor protein, and CCK-BRtx mRNA that contains exon 1a (also present in CCKBRwt mRNA) and exon 1b. The CCK-BRtx mRNA contains two open reading frames: a short open reading frame that precedes the open reading frame of the N-terminally truncated receptor. In vitro transcription/translation of the mRNAs yielded proteins of 44 kDa (CCK-BRwt), 40 kDa (CCK-BRt), and 9 kDa (CCK-BRtx). The 9 kDa product corresponded to the predicted size of the short open reading frame of CCK-BRtx. No 40 kDa product was produced by the cloned CCK-BRtx. Pharmacological analysis of CCK2 receptor ligands was performed using the cloned human CCK2 receptor (CCKBRwt) transiently expressed in COS-7 and SK-N-MC cells. The binding of YF476, YM022, AG041R, L-740,093, JB93182, PD134308, and PD136450 was analyzed by radioligand competition using [3H]L-365,260 as the labeled ligand. The binding data for four ofthe ligands fitted a one-site model (YF476, YM022, L-740,093, and AG041R), while the data for the three others fitted a two-site model (PD134308, PD136450, and JB93182) using COS-7 cell membranes in radioligand binding experiments. The data for YM022 and YF476 fitted a one-site model while the data for JB93182 and PD134308 fitted a two-site model using SK-N-MC cell membranes in the radioligand binding experiments. In the presence of a GTP-analogue, similar results were obtained. The human CCK2 receptor seems to exist in a low and/or high affmity state that does not reflect the degree ofG protein-coupling. A chicken brain CCK receptor, CCK-CHR, was cloned using a polymerase chain reaction (PCR)-based cloning strategy that included an initial PCR with deoxyinosine-containing primers targeting conserved regions in vertebrate CCK receptors, followed by rapid amplification of cDNA ends (RACE) and full-length PCR amplification. The CCK-CHR full-length PCR amplicon contained a short upstream open reading frame (uORF) followed by a long ORF encoding the 436 amino acid long receptor protein. CCK-CHR shared ≈50% amino acid sequence homology with cloned vertebrate receptors. The pharmacological profile of CCK-CHR resembled that of mammalian CCK2 receptors using agonists, but CCK1 receptors using subtype-specific antagonists. A putative cionin receptor (CioR), a new member of the CCK/gastrin receptor family was cloned from the gastrointestinal tract of the urochordate Ciona intestinalis using RACE PCR followed by full-length PCR amplification. The full-length PCR amplicon contained an uORF followed by a long ORF encoding the 526 amino acid long receptor protein. At the amino acid level, CioR shared 35-40% homology with vertebrate CCK receptors.
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